1. Field of the Invention
The present invention relates to a toner used for developing an electrostatic latent image formed by a method, e.g., electrophotography, an electrostatic recording method, a magnetic recording method, and a toner jet system recording method, and a method for manufacturing a toner.
2. Description of the Related Art
A toner has been proposed, wherein a crystalline polyester having an excellent speed of response to heat, that is, having a sharp melt property, is added and, thereby, low-temperature fixing performance of the toner is improved.
Japanese Patent Laid-Open No. 2002-287426 has proposed a toner, wherein at least 90% of dispersed domains of crystalline polyester have diameters of 0.1 to 2 μm in order to obtain excellent low-temperature fixability.
Japanese Patent Laid-Open No. 2007-093809 has proposed a toner having a core layer containing an amorphous polyester and a crystalline polyester serving as binder resins and a shell layer covering the core layer in order to enhance the thermal storage resistance and the durability while the low-temperature fixing performance on the basis of a crystalline polyester is maintained.
The toner described in Japanese Patent Laid-Open No. 2002-287426 is produced by a pulverization method. Regarding such a toner, the crystalline polyester is exposed at a toner surface. As a result, the crystalline polyester serves as a leak site, sufficient triboelectric chargeability of the toner is not obtained. If the crystalline polyester is dispersed as in the toner described in Japanese Patent Laid-Open No. 2002-287426, the glass transition point of the toner is lowered because of a plasticizing effect of the crystalline polyester. Consequently, the thermal storage resistance of the toner is degraded.
Regarding the toner described in Japanese Patent Laid-Open No. 2007-093809, toner particles are produced by an aggregation method. Therefore, a crystalline polyester may be present in a cluster without being dispersed in a toner or the content of crystalline polyester per toner particle may become nonuniform. Consequently, regarding the durability, the toner may be cracked because of the crystalline polyester present in the shape of a domain, so that there is room for improvement in the thermal storage resistance. From the viewpoint of manufacturing method of the toner, it is difficult that the shell covers all over the surface of the core particle and, thereby, the core particle is exposed partly. As a result, the crystalline polyester is exposed at the toner surface, so that the charge stability of the toner is degraded.